TUESDAY, April 7, 2026 (HealthDay News) -- The geographic atrophy (GA) enlargement rate in one eye does not consistently predict the enlargement rate in the fellow eye, according to a study published online April 2 in JAMA Ophthalmology.Leon von der Emde, M.D., from the National Institutes of Health in Bethesda, Maryland, and colleagues quantified the correlation of GA enlargement rates between fellow eyes. A post hoc analysis of the Age-Related Eye Disease Study 2 included 386 eyes of 193 participants.The researchers found that correlations in enlargement rates varied substantially by transformation used as follows: moderate for untransformed (r = 0.51; 95 percent confidence interval [CI], 0.41 to 0.61), weak-to-moderate for square root-transformed (r = 0.38; 95 percent CI, 0.25 to 0.49), and very weak for perimeter-adjusted (r = 0.11; 95 percent CI, −0.03 to 0.25) rates. In large GA, the correlation was consistently weaker than small GA: 0.30 versus 0.63 for untransformed, 0.38 versus 0.46 for square root, and 0.03 versus 0.22 for perimeter. Correlation was strongest for extrafoveal GA, intermediate for subfoveal GA, and weakest for discordant pairs for GA location using untransformed rates, with a similar pattern for square root rates. Correlation was similar for unifocal, multifocal, and discordant pairs for focality using untransformed rates."These data challenge the validity of using GA in the fellow eye as an internal control for disease progression in clinical trial design," Kelly Donovan, M.D., Ph.D., from Duke University in Durham, North Carolina, writes in an accompanying editorial.One author disclosed ties to the pharmaceutical industry.Abstract/Full Text (subscription or payment may be required)Editorial (subscription or payment may be required).Sign up for our weekly HealthDay newsletter